Not able to execute OLE Automation SPs. Execute permission denied.

Not sure what has went wrong but I'm not able to execute OLE Automation Procs like "sp_OACreate", "sp_OAMethod" etc. which was working fine for past week.
The account\login I'm using has "SYSADMIN" privilege. Also, Configuration values for "Ole Automation Procedures" has already been set to 1.
Tried with several SQL as well as Windows Login with "sysadmin" permissions but to no avail. Even with sysadmin account getting the following error:

No changes were made on SQL Level however few changes were made on OS level like, Creating and deleting SPN for the server in domain (for SQL Service Account), adding and removing SQL Service Account from following local windows account group.

Currently there is no SPN exists for the server and the SQL Services are running with windows domain account which is administrator on server but not part of any other group.

Kindly assist me as I'm neither able to find anything related to it on web nor any steps in this regard are working.

Though I can still see all these SPs in master but I can't ignore your point that they may've got corrupted somehow. Anyway you think to ensure this or rebuild them as I've already tried rebuilding as well with help of sp_addextendedproc SP (even with DAC connection) but it dint helped.

1. Restore last known good backup

2. Rebuild master database

I'm not sure if master is actually corrupt cause the instance is accessible and all other functionality and I also was able to recycle the instance twice without any hiccups. Is there anything else I should do before going in for this extreme step as this is a PROD box.

Thank you very much Vitor for your support on this. Fortunately, I was able to fix this.
The OLE automation extended procedures (ExSPs) were getting called in user defined SP and it started working again once I provided "DBO" permissions on "master" database to the user mentioned in "Execute AS" clause of that SP apart from "sysadmin". However, Two things still remained unclear for me like "how it was working earlier" (maybe the developer didn't tested it fully at first place cause calling Login (used in SP) was able to execute OLE automation ExSPs independently i.e. outside the user defined SP). And second why the calling login in the user SP required DBO permission on the "master" database even though it already had "sysadmin" permissions.
My apologies if I should've included any of these details earlier.

Seems that there are more information missing.
Who runs the SQL Server service? A local account?
The EXECUTES AS command is set to a domain user or a SQL Server user?
If it is possible post here the code.

Sorry Vitor to miss those details. All the required details are as follows:

SQL Server is running with a dedicated SQL Service Domain Account.
Created a new Domain Service Account for this purpose and the same was use in "execute as" clause of the SP.
The slightly obfuscated code is below:

I get this solution accidentally when I was trying to implement a work-around for the same. When I tried the combination of permissions mentioned above I was able to overcome the situation and things started working again. All other permission combinations which I tried earlier failed to work.

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